Battery powered devices are ubiquitous in modern society. These devices include AM/FM radios, CD players, cellular phones, portable dictation machines and the like. Many of these devices include rechargeable batteries that enable the user to prolong the life of the item without having to purchase new batteries. There are several techniques by which this recharging may be accomplished. Two of the most common include conventional outlet chargers and car chargers. The outlet charger plugs into a conventional wall outlet and translates the AC voltage to a DC voltage and maximum current level suitable for the battery being recharged. Similarly, the car chargers typically plug into a cigarette lighter and convert the 12 V DC car battery voltage to a voltage of 5 V DC and current level suitable for the battery being charged.
Of particular concern are the battery chargers for cellular telephones. As the telephones become increasingly sophisticated, the phones are increasingly sensitive to electromagnetic interference or circuit damage from errant or stray signals. One of the common classes of battery chargers for cellular telephones are called switcher chargers because they use a switch to control the output voltage. In the past switcher chargers have been of constant frequency, typically around 40 kHz, to minimize the possibility of harmonics in the 430 kHz-470 kHz range from interfering with phone operations.
There are several concerns with the construction of the chargers, namely cost and size. Obviously, the charger must also have the ability to deliver power to the recharging battery in a narrow range of acceptable values. Integrated logic chips, such as the TL494, are frequently used in switcher chargers, and act as an oscillator, a pulse width modulator, an output voltage sense amplifier, and a current limiting amplifier. However, the integrated logic chips do not presently have cable loss compensation circuitry. The integrated chips provide a currently acceptable balance between cost, size and ability to perform within acceptable parameters, but there remains a need for a viable alternative which may effectuate cost savings, decrease size, and add circuitry to counteract output voltage drop due to cable loss.